Mortgage Backed Securities are like boxes of chocolates.
Criminals on Wall Street stole a few chocolates from the
boxes and replaced them with turds.
Their criminal buddies at Standard & Poors rated these
boxes AAA Investment Grade chocolates.
These boxes were then sold all over the world to investors.
Eventually somebody bites into a turd and discovers the crime.
Suddenly nobody trusts American chocolates anymore worldwide.

Hank Paulson now wants the American taxpayers to buy up and
hold all these boxes of turd-infested chocolates for
$700 billion dollars until the market for turds returns to normal.
Meanwhile, Hank's buddies, the Wall Street criminals who stole
all the good chocolates, are not being investigated,
arrested or indicted.